Dennis competed at the 2010 Covergirl Classic in the 10-11 Hopes Division, where she placed 2nd.
2011
Dennis qualified to Junior International Elite status in 2011. She qualified to the Covergirl Classic in the Junior division. She finished 21st of 36 participants, with a score of 50.450 and therefore did not advance to the National Championships.
2012
She was scheduled to compete at the Secret U.S. Classic but withdrew with injury. Dennis advanced to the VISA Championships as she had already qualified. She had an excellent two days of competition, accumulating a two-day all-around score of 109.550.
2013–14: Junior U.S. National team
2013
Dennis returned to the Secret U.S. Classic in 2013. She finished 5th all-around, picking up a gold medal in vault and a silver on floor. Nia advanced to Nationals in Hartford, CT. She finished her two days of competition with 112.550, placing 4th in the all-around. She took home a silver medal on vault also.
2014
Dennis made her international debut in March 2014 at the City of Jesolo Trophy in Jesolo, Italy. She took home a team gold and individual silvers on the bars and all-around. She went on to compete at the 2014 Pacific Rim Gymnastics Championships in Richmond, Canada, where she won the gold medal with the U.S. team and the all-around and vault silver medals.
2015–2017: Senior International Elite
2015
Dennis' senior international elite debut came in 2015. On February 17, 2015, it was announced that Dennis had committed to UCLA for NCAA gymnastics. She will join for the 2017-18 school year and will join Olympian Kyla Ross On July 13, 2015, it was announced that Dennis was rumoured to be leaving her long-time gym Buckeye Gymnastics and has moved to Legacy Elite Gymnastics in Illinois. Following the 2015 U.S. National Gymnastics Championships, Dennis was named to the U.S. Senior National Team and was invited to the World Championships training camp.
2016
Dennis goes into the 2016 season as a second-year senior. On January 26, 2016, it was revealed that she would be the single U.S. female participant at the 2016 StuttgartFIG World Cup event, held on March 19, 2016. However, in February 2016, she tore her Achilles tendon. On June 24 and 26, Dennis competed at the P&G Championships in St. Louis, Missouri. For this event, Dennis only competed on the uneven bars. On night one, she scored a 14.500 and on night two, she scored a 14.600, giving her a score of 29.100, and placing her in twenty-fourth all-around.
